main jet removal

Mon Dec 16, 2013 12:25 am

The main jet on our cub lo-boy broke off at the cross hole when I took the carb apart.The threaded carb body hole will not allow a tapered ez out in far enough nor a 1/4in hex shank torx bit. Any ideas? Feels tight [corroded] .That end is not threaded so a left cut drillbit would be no help

Re: main jet removal

Mon Dec 16, 2013 9:17 am

Is this an IH carburetor or a Zenith? Be cautious in removal attempts to avoid damage to the carburetor body.

Re: main jet removal

Mon Dec 16, 2013 9:50 am

Image
This is the exploded view of the Zenith. Are you talking about part # 20, part # 33, or is it an IH carb?

Bob

Re: main jet removal

Mon Dec 16, 2013 9:56 am

Image
Here's the IH carb, main jet is part# 28.

Bob

Re: main jet removal

Mon Dec 16, 2013 11:01 am

It is an IH carburetor. very carefull drilling or replace the carb I'm thinking

Re: main jet removal

Mon Dec 16, 2013 11:06 am

Carefully drill out the old jet with a left handed bit. If you mess it up I can helicoil it for you.

Re: main jet removal

Mon Dec 16, 2013 11:10 am

In an IH carb, the main jet is threaded at the end opposite the hex head. You can carefully drill out the broken piece. I'd suggest spraying it with Kroil or a similar penetrant for several days. You can spray it through the idle tube hole and the idle adjustment screw hole as well as from the inside of the float bowl. I don't remember offhand what the threading is. If the threads get boogered up, they can be helicoiled, but that gets more involved as you have to enlarge the hole is the casting to get the STI tap in there. If you're not confortable doing it yourself, you can send it to one of the carb guys to have it done. Your initial description still does not sound like the main jet to me, but It may just be the way you are describing the threading.

Bob

Re: main jet removal

Tue Dec 17, 2013 12:50 pm

The plot thickens. It is an IH carb #3645?9-R9.The ?could be a 3 or 5.The main jet is #28 in the pic but the jet is stepped up on the hex end and threaded to the outer bowl shell.I will take pictures later.I think this engine was a power unit.I will check the numbers later.This moter had a wider speed range than our other cubs .idel right down and rev up high

Re: main jet removal

Tue Dec 17, 2013 3:20 pm

Here is a picture from the bottom up.main jet from a difernt cub.the broken main jet and the carb. the engine casring code is X so 1952 .Not original to a lo-boy.Would power units have different jets for more power or speed?
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Re: main jet removal

Tue Dec 17, 2013 3:54 pm

So the jet you took out is definitely no what should be there. If you remove the broken part a new jet should screw in with no problem. The shoulder on the new jet will be large enough to seal.

Re: main jet removal

Tue Dec 17, 2013 4:26 pm

The main jets all look the same, but have a different size hole on the end depending on the tractor and application.

Bob

Re: main jet removal

Tue Dec 17, 2013 7:21 pm

I don't think a new jet will seal as the hole is larger than the carb I took the regular jet from. The threaded hole on the carb is 3/16 in. Normal is likly 1/4in.I don't think the brake is fresh But it ran quite well except it was very fussy about the choke until warmed good .I never tryed a tack on it but I'm thinking 2500 rpm.[If it ain't broke don't fix it] but I thought I could improve the starting for grandkids..So is this a special carb and jet or did someone modify it? It shure had more power than our other cubs

Re: main jet removal

Tue Dec 17, 2013 8:25 pm

It's been modified.

Re: main jet removal

Wed Dec 18, 2013 7:31 am

That was just a work around after someone got too rough with the main jet and twisted it off by over-tightening it. They just rigged a plug to seal the opening. The broken jet still functions the same as it did before it was broken. If you're concerned that the the replacement jet will not seal, the best alternative may be to leave it as it is.

Re: main jet removal

Thu Dec 19, 2013 6:49 pm

Gary has nailed it.